Xapian bridge now supports offset parameter

This adds support for 'offset' parameter in the xapian bridge.
The offset specifies from where in the result set to start
returning results. We now also return totalResults and offset
as part of the response from the xapian bridge.

https://github.com/endlessm/eos-sdk/issues/1802

cool. So I'll get rid of this, and we'll do a proper fix once we have the necessary bindings in place on GLib